Engaging in and being victimized by social aggression during adolescence confers risk for emerging psychopathology and antisocial behavior. Understanding the development and consequences of social aggression may clarify the role of gender in emerging mental disorders, because girls engage in more social than physical aggression and social aggression might contribute to disorders for which girls and women have higher base rates (depression, eating disorders, and borderline personality features, Crick et al., 1999, Crick & Zahn-Waxler, 2003). Social aggression harms peers by damaging friendships or social status, and includes behaviors such as social exclusion (verbal or non-verbal), malicious gossip, and friendship manipulation (Cairns, Cairns, Neckerman, Gest, & Gariepy, 1989; Galen & Underwood, 1997; Underwood, 2003). This investigation examines the development of social and physical aggression through late adolescence, to explore the growth, change, and sequelae of engaging in and being the victim of social and physical aggression for an age range in which social aggression has rarely been studied (14 - 18). This competing continuation application proposes to follow the same sample that has been studied since age 9 in the previous project (Social Aggression: Precursors and Outcomes, 2 R01 MH063076-06). For the most complete understanding of social aggression, this research will include measures of engaging in and being victimized by social aggression. This research will employ both variable-based and person-based analyses, to examine whether social aggression might be typical adolescent behavior at low levels, but contribute to psychopathology for those who perpetrate social aggression with high frequency and for chronic victims. An important innovation of this phase of the longitudinal study will be careful assessment of social aggression in online communication by providing adolescents with handheld devices and recording and coding the content of their text messaging, Instant Messaging, and email communication. Analyzing how adolescents actually communicate online will illuminate how they use social aggression in this context, but will also provide a window into the secret world of adolescent peer culture (Greenfield & Yan, 2006, p. 392). With the multiple measures of adjustment included here, the proposed research can examine carefully how the frequency and content of adolescents' online communication relates to their well-being. This investigation will use multiple methods to measure social aggression (coding of online communication and text messaging, self-reports via telephone interviews, friend reports, parent reports, and teacher and activity leader reports) to examine growth and change in mean levels of social and physical aggression for the total sample, as well as to examine whether individuals follow different types of trajectories for engaging and being the victim of social aggression. This research will examine how growth and change in social aggression relate to the emergence of psychopathology and antisocial behavior in late adolescence. PUBLIC HEALTH RELEVANCE: This research will guide prevention and intervention efforts by identifying specific factors related to growth and change in social aggression, and by clarifying whether social aggression might be normative adolescent behavior at low levels of frequency and intensity, but still predictive of psychopathology for those who frequently perpetrate social aggression or who are chronic victims. This study will explore social aggression as a developmental precursor of adolescent psychopathology, with the long-term goal of determining whether intervening to prevent or reduce social aggression might be helpful in preventing externalizing problems, internalizing symptoms, personality disorders, and eating disorders. This study will also be the first large-scale, longitudinal investigation to examine the actual content of adolescents' online communication and the extent to which they engage in social aggression as well as other forms of communication with peers, parents, romantic partners, and even strangers; thus, these results could guide policy decisions about adolescents' access to electronic tools and online communication.